1. Field of the Invention
The present invention relates to a tool gripping mechanism for gripping a tool of a machine tool.
2. Description of the Related Art
Generally, in an ultra-precision machine tool, an automatic tool exchange system is not employed for reasons such as accuracy at the time of tool attachment and detachment and the size of the machine system. In a machining machine which performs the mold machining of an optical component, machining is generally performed with a single tool, and the deflection adjustment and dynamic balance adjustment of a tool are performed every time a tool exchange is performed.
A rotating tool is attached to a fluid bearing spindle provided in an ultra-precision machine tool. Since the fluid bearing spindle is an air turbine spindle or the like and rotates at high speed, the body of the spindle is compact. Accordingly, it is difficult to provide a complicated structure for tool exchange in the shaft of the spindle. Some ultra-precision machine tools employ shrink-fitting for tool exchange. However, in terms of temperature stability, it is not desirable to provide a heat source which heats up to almost 500° C., in or around the machine for that purpose. In particular, in ultra-precision machine tools in which an accuracy on the order of several nanometers is required, it is difficult to employ shrink-fitting for tool exchange.
Moreover, in the field of ultra-precision machining, dynamic balance adjustment is important for machining. In the case where machining is performed by rotating a spindle at a rotational speed of several tens of thousands revolutions per minute, deflection and vibration affect machining, and therefore balance needs to be adjusted to around several milligrams. Accordingly, shaft misalignment and an imbalanced state of a tool cannot be ignored. In an air turbine spindle often used in ultra-precision machining, since the phases of the tool and the shaft cannot be automatically matched with each other at present, dynamic balance adjustment needs to be performed after a tool holder is attached to the shaft.